The 4 Different Stages of Sleep

The 4 Different Stages of Sleep

When we sleep at night, we typically go through several sleep cycles. And each one of these cycles consists of 4 different stages of sleep. Let’s go through what differentiates these stages and what we know about each of them.

The 4 stages of sleep

NREM Stage 1

Stage 1 of non-rapid eye movement sleep (NREM), or dreamless sleep, occurs after you have decided to sleep and your eyes are closed. During this stage—which typically lasts between 1 and 10 minutes—you are lightly asleep, and you can quickly return to being fully awake.

Defining features

Although you are asleep, you may wake up feeling like you didn’t sleep at all.

Your body’s muscles are not inhibited yet: your eyes roll a little bit and you may slightly open your eyelids.

Your breathing slows down and your heartbeat becomes regular.

Your blood pressure and brain temperature decrease.

The hypnic jerk we sometimes experience when falling asleep, accompanied or not by the sensation of falling down, happens during this stage. Some say it is a vestigial reflex humans developed during the evolutionary process to prevent them from falling off the trees they slept in.

Did you know?
People with irregular sleeping habits tend to have these hypnic jerks more often.

NREM Stage 2

When NREM Stage 2 sleep kicks in, things get serious!

Defining features

Stage 2 sleep, which usually lasts about 20 minutes, is characterized by a slowing heart rate and a decrease in body temperature. Your body reduces its activity to prepare you to go into a deep sleep.

It becomes harder to wake you up.

Your brain starts to emit larger waves.

Your blood pressure also decreases, and other metabolic functions slow down too.

The 2 first stages of NREM Sleep together are often referred to as light sleep.

Did you know?

We spend most of our nights in Stage 2 sleep (around 45% of total sleep duration).

Steel HR

REM sleep is also known as “paradoxical sleep.” This is because the brain waves emitted during this stage seem contradictory to sleep: Although you are sleeping, your brain waves look at lot like what can be recorded when you are fully awake. Another aspect of this paradox is the fact that even though your brain shows heightened activity, most of your muscles are paralyzed.

What the brain waves of each stage of sleep looks like

The image above shows the different stages of sleep, as they appear when you record your brain waves.

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